1. The field of art to which the invention pertains comprises the art of valves including seals and packing therefor.
2. The prior art to which the invention is directed includes the art of valves and particularly butterfly valves being a type in which a usually circular closure vane or disc is mounted either centralized or offset for rotation in the body flow passage between an open and closed position. Construction for such valves commonly consists of a body and/or closure vane of cast iron or the like operable by means of an operator shaft extending through a bore in the body wall to externally thereof.
Normally supporting the operator shaft is a sleeve-like journal suitably packed to prevent leakage of line content from the flow passage past the journal to atmosphere. A self-packing seal is frequently supported on the shaft intermediate the vane and journal for preventing leakage of line content therepast. While this combination of components is known to perform well for service applications such as water distribution, it has not been found suitable in application for gas service or the like. Not only is substantially higher gasket pressure required to prevent gas leakage from the valve passage than is generally possible with a self-sealing type gasket, but internal leakage from secondary sources is a significantly greater problem with gas than with water. The source of secondary leakage has only recently been identified with porosity of the vane and/or functional failure of the shaft seals enabling pressurized line content access to the shaft surface either through the vane cavity or past a non-functioning seal located elsewhere. In either situation, the gas tends to travel internally of the vane along the shaft internally of the journal through the operator to atmosphere.
Because of the possible combustible nature of the gas line content, sealing against leakage in any form is critical. Despite recognition of the problem, solutions heretofore have included a variety of self-sealing gaskets to prevent leakage and porosity testing each vane under pressure and/or other testing to insure against secondary leakage. As might be expected, neither has proven satisfactory because of the general unreliability of the self-sealing gasket and the high expense which such tests incur, not to mention the high scrap cost attributed to those vanes rejected by the test.